Nervous about nukes again? Here’s what you need to know about The Button. (There is no button.)

“The football” — the briefcase that contains instructions for launching a nuclear strike — is held by a military aide as President George W. Bush and first lady Laura Bush wave from the steps of Air Force One in Madrid in 2001. (David Hume Kennerly/Getty Images)

Let’s talk fingers and buttons.

“He shouldn’t have his finger on the button,” Hillary Clinton said about Donald Trump in June.

“I will not be a happy trigger like some people might be,” Trump said on the “Today” show in April, adding: “I will be the last to use nuclear weapons.”

“A man you can bait with a tweet is not a man we can trust with nuclear weapons,” Clinton said during her convention speech July 28 in Philadelphia.

On Wednesday, MSNBC’s Joe Scarborough claimed that Trump asked a foreign-policy adviser three times why, if we have nuclear weapons, can’t we use them? (A Trump spokeswoman denied that this happened.)

One reason: The detonation of 100 nuclear warheads — there are about 15,000 on the planet right now — could kill 2 billion people, according to International Physicians for the Prevention of Nuclear War.

In a presidential campaign, America confronts its own destructive power and the single person entrusted with it: Whose finger is on the button?

Fact check: There is no button.

There is a briefcase, though.

It follows the president everywhere — onto Air Force One, onto the golf course, onto elevators. Inside is a manual for conducting nuclear war. A how-to, really.

The briefcase is aluminum, 45 pounds, clad in leather and descends from a line of durable, airtight cases made specially for Erle P. Halliburton, the oil-field engineer who founded the company that would become infamous because of its associations with Dick Cheney, the Iraq war and the Deepwater Horizon oil leak.

Carrying the briefcase is a job shared among five military aides, one from each branch of the U.S. armed forces. The manual inside is more like a takeout menu, but instead of picking between numbered Chinese dishes, the president would choose cities or military installations in, say, Russia or China (or both) to attack.

Zero Halliburton is the company that has been known to make these briefcases, but it’s not certain about the current football; the White House, which refused comment on football matters, bought a bunch about eight years ago and hasn’t yet ordered more. Zero Halliburton has also supplied cases as props for the TV series “24” and the Arnold Schwarzenegger movie “True Lies.” In both, nuclear weapons explode with an unsettling degree of ease. Since the beginning of the atomic age, it’s an image we’ve seen again and again. In popular culture, nukes are detonated by keys, buttons and — in the case of “The Dark Knight Rises” — countdown clocks.

The nuclear briefcase, carried by a military aide to President George W. Bush in August 2005 on a trip to Texas. (Mark Wilson/Getty Images)

It’s more complicated in real life, but not less scary. To authorize an attack, the president would use a card of verification codes that is, ideally, on his person at all times.

The briefcase is referred to as “the football,” the card as “the biscuit.”

Jimmy Carter is rumored to have sent the biscuit to the dry cleaners accidentally.

After Ronald Reagan was shot, hospital staff cut off his suit and the biscuit fell with it to the ground; it was later scooped up as evidence by the FBI, which initially refused to return it to the military.

The biscuit was presumably in one of President Obama’s pockets in May as he became the first sitting president to visit Hiroshima, where 160,000 Japanese people were killed or injured by the first combat use of a nuclear weapon 71 years ago Saturday.

“We have a shared responsibility to look directly into the eye of history,” Obama said there, “and ask what we must do differently to curb such suffering again.”

At the president’s disposal right now are a little over 900 nuclear warheads deployed on various “delivery vehicles” around the planet. Some sit atop missiles buried in the ground in Montana, North Dakota, Wyoming, Nebraska and Colorado. Some are carried by submarines that are patrolling the North Atlantic and western Pacific. Others are ready to be loaded onto aircraft in Missouri, North Dakota, Belgium, Germany, Italy, the Netherlands and Turkey.

Some of these warheads can be launched within minutes of the president’s order, hit anywhere in the world within a half hour, and deliver 20 times the explosive force of the bomb dropped on Hiroshima. The president can order this without consulting Congress, without being checked by the Supreme Court.

“The longer I’m in the Senate, the more I fear for a major error that somebody makes,” Sen. Dianne Feinstein (D-Calif.) told CQ last month after a hearing on plans to develop a new nuclear cruise missile that could cost $20 billion. “One man, the president, is responsible. He makes an error and, who knows, it’s Armageddon.”

America just nominated two people to inherit this ultimate power. The winner will also inherit an unnerving history of close calls.

In 1961, a B-52 bomber broke up over North Carolina and dropped two warheads to the earth; each had the potential to explode with the force of 200-plus Hiroshimas.

In 1979, Carter’s national security adviser, Zbigniew Brzezinski, was told that hundreds of missiles were on their way from the Soviet Union; a minute before he called the president to coordinate a devastating response, he was told that the military had misinterpreted a training exercise.

In 1983 and 1995, Moscow came within minutes of retaliating against false alarms — the first prompted by sunlight reflecting off clouds, the second by a NASA research rocket.

In 2007, six warheads were mistakenly flown from North Dakota to Louisiana before anyone realized that nuclear weapons had been in the air over the United States.

In 2012, an 82-year-old Catholic nun and two fellow peace activists easily intruded into a weapons site in East Tennessee that is nicknamed “the Fort Knox of Uranium” and hosts perhaps the biggest stockpile of fissile material in the world.

Obama, in his first speech abroad as president in 2009, said humanity should seek “the peace and security of a world without nuclear weapons.” Now we’re readying to spend $1 trillion over the next 30 years to modernize the U.S. arsenal, according to the James Martin Center for Nonproliferation Studies, and essentially keep it operational into the 2080s.

And the Doomsday Clock, a symbolic estimation of global peril, has ticked closer to the midnight of Armageddon since 2010. It was six minutes to midnight then. In 2012, the Bulletin of the Atomic Scientists moved the clock to five minutes to midnight. Last year, to three.

Ticktock. Ticktock.

What if Trump is elected? Clinton?

“I have one of the great temperaments,” Trump said on ABC Sunday in reply to Clinton’s line about baiting him with a tweet. “I have a winning temperament.”

North Korea tested a nuclear bomb in January and may be readying another.

Troops are massing along European borders with Russia, which deployed nuclear-capable forces after it annexed Crimea in 2014. In May, NATO began operating a U.S. missile-defense system in Romania, just across the Black Sea.

From 2010 to 2014 the National Nuclear Security Administration was hacked 19 times, according to documents obtained by USA Today.

In the past two years there have been 2,700 cases of illicit trafficking of radiological material around the world.

Former defense secretary William Perry witnessed three false alarms during his service in government, which ended nearly 20 years ago. And yet: “The likelihood of a nuclear catastrophe is greater today than during the Cold War,” Perry said last month in Washington at a dinner with journalists.

There’s the possibility of accident or miscalculation, he said.

Or the threat of nuclear terrorism.

Or tensions between India and Pakistan.

Then again, the scariest thing about the football and the biscuit may be that they exist at all. So thought the late Jesuit priest and peace activist Richard McSorley, who once pegged nuclear weapons as the father of all conflict — as devices that damage even if we don’t detonate them.

“The taproot of violence in our society today,” he wrote, “is our intent to use nuclear weapons. Once we have agreed to that, all other evil is minor in comparison.”

One’s mind goes to armed drones. To assault rifles. To violence against women, against police, against protesters.

“So if you see somebody getting ready to throw a tomato, knock the crap out of them, would you?” Trump told his supporters at a rally earlier this year. “Seriously.”

There may be only one biscuit and one football, but there are buttons everywhere.

Correction: An earlier version of this article misstated the number of nuclear weapons currently deployed by the United States. This version has been updated.

Dan ZakDan Zak is a reporter for The Washington Post. He writes a wide range of news stories, narratives and profiles from local, national and foreign assignments, from the Academy Awards to Fallujah, Iraq. He joined The Post in 2005. Follow